1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a metal film.
2. Description of the Prior Art
Continued efforts for refined design and high density configuration of the structure for semiconductor elements such as insulated gate field effect transistor (referred to as MOS transistor hereinafter) are still being pushed vigorously presently. As for the refinement, semiconductor elements formed with 0.13 to 0.18 xcexcm rule are generally adopted at present, and memory devices, logic devices or the like based on this design rule are being put to practical use or being under development. Such a refinement is the most effective technique for enhancing the performance or multifunctional capability of the semiconductor devices through high integration and fast operation, and is an indispensable step for the manufacture of the future semiconductor devices. For the purposes of high integration, fast operation, multifunctional capability and low power consumption of the semiconductor devices, it is to be realized that the formation of metal films plays an extremely important role.
For example, accompanying high integration of ULSIs, groove wirings employing a conductive layer of copper (Cu) or a copper alloy have been proven to be very effective due to reduced resistance or enhancement in the resistance to electron migration of these wirings. In this case, it is indispensable to prevent the diffusion of copper that gives an adverse effect to the semiconductor elements, and hence, there arises a need for a barrier metal which prevents the diffusion of copper. In addition, a film of such metal as titanium (Ti) or a barrier metal such as titanium nitride (TiN) is indispensable for fine contact holes, through holes or the like that connect the wiring layers in a multilayer wiring structure. Moreover, for memory cells that is composed of one transistor and one capacitor, of a DRAM, an extremely thin barrier metal of titanium nitride or the like is also indispensable.
Such a metal film as described in the above is formed generally by a sputtering method. However, with the refinement of the semiconductor elements as mentioned in the above, an improvement in the step coverage becomes necessary in the formation of a metal film. With this in mind, a metal film, such as a titanium nitride film or a titanium film, is being formed by means of a chemical vapor deposition (CVD) method. However, the film formation temperature in this case has to be set considerably higher than in the case of the sputtering method.
A CVD device for the formation of such a metal film has, in a normal mass production facility, a plurality of reaction chambers (referred to also as process chambers). In other words, the CVD device has a capability for multichamber processing by which formation of various kinds of films can be handled by means of a single unit of the device.
Referring to FIG. 3, such a multichamber device will be described. Namely, a multichamber device 1 is equipped with a load lock chamber 2, a separate chamber 3, process chambers 4, 4a and 4b, and the like. In forming a metal film on a semiconductor substrate (referred to also as a wafer) made of silicon or the like, as described in the above, the wafer is loaded and unloaded onto and from the multichamber device through the load lock chamber 2. The wafer is transferred between the load lock chamber and the separate chamber, and between the separate chamber and the process chamber, respectively, by means of an arm. Here, in the multichamber device, the oxygen partial pressure and the concentration of moisture within the load lock chamber and the separate chamber are set low by increasing the degree of vacuum in these chambers.
In the following, the formation of a titanium nitride film as well as a titanium film using a single unit of the multichamber device will be described.
As shown in FIG. 3, a wafer is transferred into the separate chamber 3 through the load lock chamber 2 in order to form a titanium nitride film on the wafer. Here, the degree of vacuum of the separate chamber 3 is set at about 10 Pa. Then, the wafer is brought into the process chamber 4 to have a titanium nitride film formed on it.
In the formation of a titanium nitride film, the interior of the reaction chamber, namely, the process chamber 4, is held initially at a deposition temperature (TD) of about 700xc2x0 C., and the following reaction gas is introduced into the process chamber 4. Namely, first gaseous titanium tetrachloride (TiCl4) and gaseous ammonia (NH3), then gaseous nitrogen (N2) are introduced into the process chamber 4 to obtain the gaseous pressure within the reaction chamber of about 40 Pa. In this way, a titanium nitride film with thickness of about 50 nm is formed on the silicon substrate.
Now, in a mass production facility, after the formation of the titanium nitride film for a group of semiconductor wafers, namely, for one lot of the products (25 pieces of wafers, for example), there may be scheduled a case in which a titanium film is to be formed for another lot of products within the multichamber device. Thus, this time a situation arises where a titanium film is to be formed in the process chamber 4a for the lot of products by means of a plasma excited CVD (PECVD) method, for example.
During the formation of the titanium film the process chamber 4 is in the standby period for the next group of semiconductor wafers. At this point, the temperature within the process chamber 4 is lowered to a standby temperature (TS) as shown in FIG. 4. This is done so for the purpose of preventing the titanium nitride film, stuck on the inner wall of the process chamber 4 during the formation of the titanium nitride film, from being oxidized by the high temperature employed in the process. In the conventional method, the rate of the temperature drop in the transition from the film deposition temperature to the standby temperature is set at about 30xc2x0 C./min in consideration of the mass productivity of the products.
When, after the completion of formation of the titanium film, formation of the titanium nitride film for the next group of the semiconductor wafers is about to be started again within the process chamber 4, the temperature in the process chamber 4 is raised from the standby temperature to the deposition temperature as shown in FIG. 4 to start the formation of the titanium nitride film for the group of the products. In the mass production of the semiconductor device, different kinds of metal films are formed using a single unit of mass production device as described in the above.
In the conventional manufacturing method of the semiconductor device, the rate of temperature drop from the deposition temperature to the standby temperature is large as mentioned above, and particles are liable to be generated in the process chamber for the formation of the titanium nitride film. Nonetheless, the effect of the method of temperature drop has not been examined carefully enough.
The inner wall of the conventional process chamber is subjected to an alumite treatment to have a coating of an alumina film. When the temperature within the process chamber is varied under such a circumstance, a metal film such as the titanium nitride film stuck on the inner wall of the process chamber tends to be peeled off the inner wall of the process chamber due to contraction or expansion.
A detailed examination by the present inventor using a metal film formation device as described above revealed that the peeling of the metal film depends heavily on the rate of temperature drop from the deposition temperature to the standby temperature. It has been considered that the generation of particles in the conventional method mentioned above is a result of an almost uncontrolled relatively large rate of temperature drop.
Generation of such particles deteriorates the yield of mass production of the semiconductor device, and the size of the particles that affects the mass production yield becomes smaller with the enhancement of the refinement and high performance, as mentioned above, of the semiconductor device. In this respect, the control of the rate of the temperature drop on the level of mass production becomes extremely important.
Furthermore, in the conventional technique, the dispersions between lots of the film thickness and the film quality of a metal film such as titanium nitride film are large, which seems to be a result also of the peeling of the metal film.
Object of the Invention
It is the object of the present invention to provide a method of manufacturing a semiconductor device that makes it possible to prevent generation of particles in the film formation of a metal film on the mass production level.
Summary of the Invention
The method of manufacturing a semiconductor device according to this invention includes a step of forming a metal film on a group of semiconductor wafers by keeping the interior of a chamber of a film formation device at a deposition temperature of the metal film, and a step of then lowering the temperature of the interior of the chamber to a standby temperature at a constant rate and holding the interior of the chamber at the standby temperature until the film formation treatment of the next group of the semiconductor wafers.